The only RA operation, that seems to allow view updates is renaming.
However, consider

rename( R(x,y), x->y )

Is renaming into the existing attributes allowed (then renaming is
projection, which is not updatable)?

I suggest that the idea that we focus on basic relational algebra
operators, figure out which updates of these are legitimate, then
leverage this knowledge for complex view updates is fundamentally
wrong. Consider a "pivot" view:

This is a perfectly updatable view, yet your approach would fail to
discover how to translate its update to the base table. (This pivot
operation is a recurrent theme in data exchanges)

Then, there are constraints, "simultaneous" updates of multiple views.
There is simply no way a naive analysis (of how RA operations may
behave under view update) could possibly provide any insight to the
problem.
Received on Fri Sep 04 2009 - 13:37:30 CDT